Medical technology has long endeavored to be able to occlude septal defects, for instance atrial septal defects, with non-surgical transvenous catheter intervention, in other words, without having to perform an operation in the literal sense. Various different occlusion systems have been proposed, each with their own advantages and disadvantages, without any one specific occlusion system having yet become widely accepted. In making reference to these different systems, the following will use the terms “occluder” or “occlusion device.”
In all interventional occlusion systems, a self-expanding umbrella system is introduced transvenously into a defect to be occluded in a septum. This type of system might comprise two umbrellas; one positioned at the distal side of the septum, for example the side farthest from the median plane of the body/heart), and one at the proximal side of the septum (i.e. the side closer to the median plane of the body), whereby the two umbrella prostheses are subsequently fitted into a double umbrella in the septal defect. Thus, in the assembled state, the occlusion system usually consists of two fixed umbrellas connected to one another by means of a short peg which passes through the defect.
However, a disadvantage to such known prior art occlusion devices turns out to be the relatively complicated, difficult and complex implantation procedure. Apart from the complicated implantation of the occlusion system in the septal defect to be occluded, the umbrellas utilized are fundamentally susceptible to material fatigue along with fragment fracture. Furthermore, thromboembolic complications are frequently to be anticipated.
With another type of occlusion device, the so-called Lock-Clamshell umbrella system, two stainless steel, preferably Dacron-covered, umbrellas are provided, each stabilized by four arms. This type of occluder is implanted into the patient through a vein. However, seen as problematic with the Lock-Clamshell occluder is the fact that the insertion instruments necessary to implant the device need to be of relatively large size. A further disadvantage is that many different occluder sizes are needed in order to cope with the respective proportions of the septal defects to be occluded. It thus turns out that the umbrellas do not flatten out completely in the inserted state if the length or the diameter of the crosspiece inserted into the defect is not of an optimum match. This results in incomplete endothelialization. It has furthermore been shown that over a longer period of time, many of the systems implanted into patients' bodies will exhibit material fatigue and fractures in the metallic structures due to the substantial mechanical stresses. This is especially the case given permanent tension between an implant and the septum.
In order to overcome these disadvantages, self-centering occlusion devices have been developed which are inserted into the body of the patient and introduced into the septal defect to be occluded by way of a minimally-invasive procedure, for example using a catheter and guide wires. Their design is based on the principle that the occlusion device can be tapered to the dimensions of the insertion instrument and/or catheter used for the intravascular surgical procedure. Such a tapered occlusion device is then introduced by catheter into the septal defect to be occluded, respectively into the shunt of the septum defect to be occluded. The occluder is then discharged from the catheter, upon which the self-expanding umbrellas, retention discs respectively, subsequently unfold against the two sides of the septum. The umbrellas in turn comprise fabric inserts made from or covered by, for example, Dacron, with which the defect/shunt is occluded. After a few weeks or months, the body's own tissue more or less completely envelops the implants remaining in the body.
An example of this type of self-centering occlusion device is known from U.S. Pat. No. 5,725,552, which describes an occlusion device known as the “Amplatz occluder.” This known system will be briefly described below with reference to FIGS. 15a to 15c. Specifically, FIG. 15a shows a tubular braiding known from the prior art, for example said U.S. Pat. No. 5,725,552, as the base structure or starting body for manufacturing this type of known occlusion device, whereby each end of the tubular braiding needs to be held in a respective holder. FIG. 15b depicts a side sectional view of the right side of a known PFO-type occlusion device from the prior art, for example said U.S. Pat. No. 5,725,552, with the occlusion device being made from a tubular braiding in accordance with FIG. 15a, while FIG. 15c shows a right-side sectional view of a further ASD-type occlusion device likewise known from U.S. Pat. No. 5,725,552, with this occlusion device also being made from a tubular braiding in accordance with FIG. 15a. 
To be understood by the term “PFO-type” as used herein is an occlusion device for treating a patent foramen ovale (PFO) while the term “ASD-type occlusion device” refers to an occlusion device for treating atrial septal defects.
The known occlusion devices consist of a braiding of a plurality of fine, intertwined nitinol wire strands in the shape of a yo-yo. Each braiding is manufactured in its initial form as a rounded braiding having loose wire ends both at its leading end (its proximal side, respectively) as well as at its trailing end (its distal side, respectively). During the subsequent processing of the rounded braiding, these loose ends must then be gathered into a collar and welded together. After the appropriate processing, both the proximal side as well as the distal side of the finished occluder exhibit a protruding collar. Dacron patches are sewn into the distal and proximal retention umbrellas and the interposed crosspiece. Because of the memory effect of the nitinol material used, the two retention umbrellas unfold by themselves upon exiting the catheter, initially in a balloon-like intermediate stage, whereby the retention umbrellas ultimately positioned on the two sides of the septum eventually assume a more or less flattened form. The crosspiece centers itself automatically into the shunt to be occluded as the umbrellas expand.
Because the collar protrudes past the proximal retention area of the occluder, the problem arises that the inserted implant causes embolic-related problems, in particular consecutive embolization. Because portions of the occlusion device protrude past the septum wall and are in continuous contact with the blood, defense system reactions are also a frequent occurrence. Furthermore, a complete endothelialization of the occluder implant is often prevented.
An occlusion device of the type indicated at the outset as well as a method for manufacturing such an occlusion device is additionally known from WO 2005/020822 A1. The occlusion device described therein essentially consists of a braiding of thin wires or threads made from a material having shape-memory function. In the expanded state, the known occlusion device exhibits a proximal and a distal retention area as well as a cylindrical crosspiece interposed between the two.
Because the proximal retention area of the braiding exhibits a form which is open to the proximal end in this prior art, it basically allows the rim of the proximal retention area to lie flat against the septal wall when the occlusion device is in the inserted state while the retention area does not protrude beyond the septal wall.
The manufacturing process according to WO 2005/020822 A1 utilizes a braiding technique which forms a tubular braiding open to the top, which need only be provided with a holder for bundling the braiding's threads or wires on one end, while at the opposite end, the braiding's threads or wires are intertwined from their center. It thus becomes possible to produce a braiding to serve as the base structure for the known occlusion device, whereby the proximal retention area of the base structure exhibits a form open to the proximal end.
To further define the occlusion device known from WO 2005/020822 A1 more specifically, particular reference is made to FIGS. 16a to 16c. In detail, FIG. 16a shows a tulip or bell-shaped braiding having a distal holder known, for example, from WO 2005/020822 A1. FIG. 16b depicts a sectional view of the right side of a PFO-type occlusion device known from WO 2005/020822 A1, whereby the occlusion device is made from a tubular braiding in accordance with FIG. 16a. FIG. 16c finally shows another sectional view of the right side of an ASD-type occlusion device known from WO 2005/020822 A1, with the occlusion device likewise being made from a tubular braiding in accordance with FIG. 16a. 
In the case of these occlusion devices known from WO 2005/020822 A1, it has proven disadvantageous for the braiding on the proximal end to exhibit an opening which needs to be spanned by, for example, a Dacron insert or a cloth so that the finished occlusion device will no longer be open at its proximal end. Producing such an occlusion device necessitates quite a complex manufacturing process, and one which is thereby cost-intensive. Furthermore, different materials, namely the materials of the braiding and of the Dacron insert or cloth need to be force-fit to one another. Such joints are inherent weak points in terms of material fatigue. Thus, this known type of occluder has an increased risk of material fatigue along with fragment fracture. It has furthermore been shown that such an implanted system can exhibit material fatigue and fractures in the joints between the metallic structures and the Dacron insert after a longer period of time within a patient's body, stemming from the considerable mechanical stresses. This is especially the case when there is permanent tension between the braiding and the insert.
Moreover, thromboembolic complications need to be considered with the occlusion devices known from WO 2005/020822 A1. While the known system enables the rim of the proximal retention area to lie flat against the septal wall and not have the retention area project beyond the septal wall when the occlusion device is in the inserted state, the proximal end of the known occlusion device nevertheless exhibits a manufacturing-contingent opening at the proximal wall axial to the crosspiece. Even if this opening is—as described above—closed with a Dacron insert, for example, the known system cannot prevent the finished occlusion device from having at least one remaining trough-shaped recess or sometimes even components protruding in the proximal retention area of the occluder, these being at the very location where the opening closed with the Dacron insert is disposed.
Along with trough-shaped recesses and protruding components comes yet another problem, that of the inserted implant causing embolic-related problems, in particular consecutive embolization. These embolic-related problems arise especially when the patient is suffering from so-called atrial fibrillation of the heart. This is a condition in which frequent excitation of the heart's upper chambers results in their not contracting. As a consequence of the left and right halves of the heart being deprived of contraction, the blood is ineffectively swirled and mixed and thrombi can form in the atrium. A considerable risk when atrial fibrillation causes thrombi to form in the atrium is that these thrombi can be carried along in the bloodstream and enter the arterial circulation. Apoplectic strokes, occurring in approximately 5% of atrial fibrillation patients each year, are a particular consequence of this embolization when not chronically treated with so called dicumerol, a blood anticoagulant. However, anticoagulating the blood with so called dicumerol is also not without risks. One side effect of dicumerol treatment is increased bleeding such that there are contraindications for this treatment for approximately 20% of all atrial fibrillation patients and the patients thus have to hazard the risk of a stroke when weighing the bleeding/stroke risk.
The present invention therefore addresses the problem of refining such an occlusion device as known to medical technology and described in WO 2005/020822 A1 so as to overcome the disadvantages cited above. A particular objective is the providing of an occlusion device applicable to occluding defects of different sizes, whereby implantation of the occluder is to be a simple procedure. Furthermore, the occurrence of such usual occluder complications such as dislocation, partial embolization or occluder material fatigue is to be reduced to the greatest extent possible. Above and beyond that, an occlusion device is to be provided which ensures occlusion of a septal defect with as few portions of the occlusion device as possible protruding past the septum wall so as to avoid the associated and above-cited complications.